LOWELL — An employee of supermarket chain Market Basket has filed a federal complaint against the company for threatening to fire protesting workers.

Lowell resident Karen Bostwick says in her complaint filed with the National Labor Relations Board office in Boston that Market Basket is "violating the right to picket and strike" and threatening to fire protesting employees "created a "hostile work environment."

Bostwick works at the company's Tewksbury headquarters.

Thousands of the 71-store chain's workers have walked off the job in an effort to have ousted CEO Arthur T. Demoulas reinstated.

A spokesman for Market Basket said he could not comment because the company has not seen a copy of the complaint.

Arthur T. Demoulas is close to completing a purchase of shares of the company owned by rival family members.